Timber Thickness

When buying lumber or timber it’s very easy to become confused and end up with something your not satisfied with or even worse wood you can’t use. In this video Chris Marshall from Woodworker’s Journal looks at some the causes of misunderstanding and suggests some tips to overcome the problems.

In this example he is looking for some 3/4″ (19mm) timber for window frames. He needs some leeway in order to make it flat and true so looks at “four quarter” or 1″ (25.4mm). This size refers to the size of the timber before it is given its final surfacing and so is usually between 13/16″ (20mm) and 15/16″ (24mm).

Chris recommends taking a tape measure with you to the lumber store (or vernier calipers that he uses in the video).  If you’re buying  out of the area check the finished thickness specified and  if its not phone up and ask.

Buying timber rough sawn or unfinished is the best deal as 1″ (25.4mm) timber will be very minimum 1″ and you will have complete control over the finishing and final size.  An added bonus is that it can be one of the cheapest ways to buy lumber.

Buying timber from a home centre or DIY store you get timber that has been finished on all four sides and is the exact measure so there is no leeway for making it flat or true, especially as it could change shape when you get it into a warm dry workshop.


Wow, that was a great video that I just saw. Would all timber supplies be measured for their thickness before being sent to the customers? It seems like it would be more convenient to do for the customers. 

Rose Nickelson
Rose Nickelson

My daughters really want a tree house, so me and my husband are going to build them one. I went to get some wood for it this past weekend and I got so confused at the store. I really found your tips on buying rough timber super helpful. It seems like I am going to be able to know what wood to get the next time I go to the show.